Fertilizers have been used for many years to supplement nutrients in growing media. In recent years the art has focused on techniques to deliver controlled amounts of plant nutrients to the soil or other growing media. It is recognized, for example, that controlling the release of plant nutrients such as nitrogen from highly soluble fertilizer granules is desirable because releasing the nutrients over an extended period of time achieves advantages which include increased efficiency of fertilizer use by plants, reduced application costs since fewer applications of fertilizer are required and reduced nutrient loss caused by leaching and denitrification.
U.S. Pat. No. 5,538,531 (Hudson) teaches a controlled release, particulate fertilizer product having a water soluble fertilizer central mass encased in a plurality of water insoluble, abrasion resistant coatings. At least one inner coating is a urethane reaction product derived from reacting recited isocyanates and polyols. The outer coating is formed from an organic wax.
U.S. Pat No. 6,358,296 (Markusch et al.) teaches a slow-release polyurethane encapsulated fertilizer using oleo polyol(s). U.S. Pat. No. 5,851,261 (Markusch et al.) provides a process for the production of polyurea encapsulated fertilizer particles comprising applying an isocyanate-reactive component containing at least two amine groups to the fertilizer particles, and applying a polyisocyanate to the amine coated particles to form polyurea coated particles.
Sulfur containing isocyanate compositions and a process for the production of encapsulated fertilizer compositions are described in U.S. Pat. No. 6,152,981 (Markusch et al.). The fertilizer compositions are prepared by applying a mixture of sulfur and an isocyanate to the fertilizer and then applying an isocyanate-reactive material. U.S. Pat. No. 5,599,374 (Detrick) describes a fertilizer composition wherein a sulfur coating is applied to a fertilizer core, and thereafter a polymer coating is applied over the sulfur.
U.S. Pat No. 6,231,633 (Hirano et al.) teaches a granular fertilizer coated with a thermosetting resin coating that may be urethane and a hydrophobic compound, which may be wax. U.S. Pat. No. 6,663,686 (Geiger et al.) teaches a slow-release polyurethane encapsulated fertilizer using polyurethane and wax.
U.S. Pat. No. 6,039,781 (Goertz et al.) teaches that it is also known in the art to pre-coat particulate plant nutrient with organic oil and particles as a means to improve the release profiles of the particulate plant nutrient.
U.S. Pat. No. 6,338,746 (Detrick et al.) describes a process of first coating a fertilizer with a polymer, then coating the polymer with sulfur and thereafter applying a polymer coating. The polymers are described in U.S. Pat. Nos. 4,711,659 (Moore), 4,804,403 (Moore) and 5,374,292 (Detrick). These polymers require that the substrate contains a minimum quantity of reactive —NH2 groups. Thus, these are not applicable to all fertilizer compositions for which slow release properties may be desirable.
Although polymer coated fertilizers as above described have received substantial attention, they are expensive to manufacture. There is a need in the art to provide controlled released fertilizer formulations that are abrasion resistant, and that reduce the cost of fertilizer production. Additionally, it would be desirable to have a controlled release fertilizer and process for production thereof which would allow for the ready customization of the release rate profile of a given particulate plant nutrient having applied thereto a given amount of urethane coating(s). It would also be desirable to be able to achieve a desirable release rate profile for a given particulate plant nutrient using significantly reduced amounts of coating materials.